Hydrogen explained: from colours to carriers

Hydrogen is a versatile energy carrier and a key enabler of the energy transition. it can be produced in different ways, used across multiple sectors and transformed into other molecules, to support decarbonisation.

Understanding hydrogen: the basics

Hydrogen (H₂) is an odourless, colourless, non-toxic gas and the most abundant element in the universe. On Earth, however, it is rarely found in its pure form and must be extracted from other molecules such as water (H₂O), methane (CH₄) or ammonia (NH₃), which requires energy.

Hydrogen is not a primary energy source but an energy carrier, meaning it stores and transports energy generated from other sources such as renewables, nuclear power or fossil fuels.

The colours of hydrogen

Hydrogen itself is always colourless. The different “colours” simply refer to the production method (and associated emissions).

Grey hydrogen

• Produced from natural gas through steam methane reforming (SMR) or autothermal reforming (ATR)
• Its production releases CO₂ into the atmosphere
• Currently the most widely produced form of hydrogen worldwide

Blue hydrogen

• Produced similarly to grey hydrogen, preferably through ATR
• CO₂ emissions are highly concentrated, which facilitates their capture for further storage or use
• Emits significantly less CO₂ (up to 80–95% reduction compared to grey hydrogen)
• It can be rapidly deployed in significant volumes such as those required on an industrial scale

Green hydrogen

• Produced using renewable electricity (wind, solar, hydro)
• Generated via electrolysis (splitting water into hydrogen and oxygen)
• Emits almost no greenhouse gases during production

Turquoise hydrogen

• Produced from methane via pyrolysis
• Process generates solid carbon (with many industrial applications) instead of CO₂
• Considered a low carbon alternative

Pink hydrogen

• Produced using electricity from nuclear power
• Generated via electrolysis
• Offers stable and continuous production
• Also considered low carbon

White hydrogen

• Naturally occurring hydrogen found underground
• Still rare but has potential for future energy supply

EU perspective

The European Union does not use colour terminology. Instead, it classifies hydrogen into:

• Renewable Fuel of Non-Biological Origin (RFNBO): e.g. green hydrogen
• Low carbon: e.g. blue, pink, turquoise
• Fossil-based: e.g. grey hydrogen

Hydrogen and its derivatives

Around 100 MTPA of hydrogen are used worldwide, mainly to produce ammonia and methanol and for petroleum refining. Hydrogen is often transformed into other molecules (derivatives) to facilitate its storage and its transport over long distances.

Ammonia (NH₃)

• Produced by combining hydrogen with nitrogen
• Widely used in fertilisers and industrial processes
• Acts as an efficient hydrogen carrier, especially for long-distance transport

Methanol (CH₃OH) and synthetic fuels

• Hydrogen can be combined with carbon to produce methanol and synthetic hydrocarbons
• Used in the production of plastics, chemicals and fuels

Why derivatives matter

• Transporting pure hydrogen over long distances is challenging due to its low volumetric density
• Derivatives such as ammonia or synthetic methane allow for:
  • Easier storage
  • Maritime transport
  • Integration into existing infrastructure